1. Field of the Invention
The present invention relates generally to transferring wafers among modules of semiconductor processing equipment, and more particularly to dynamic alignment of each wafer with a support blade that carries the wafer, wherein dynamic alignment apparatus and methods determine the location of a center of the wafer with respect to a center of the blade as the blade moves the wafer through a slot from one module to another module.
2. Description of the Related Art
In the manufacture of semiconductor devices, process chambers are interfaced to permit transfer of wafers or substrates, for example, between the interfaced chambers. Such transfer is via transport modules that move the wafers, for example, through slots or ports that are provided in the adjacent walls of the interfaced chambers. Transport modules are generally used in conjunction with a variety of wafer processing modules, which may include semiconductor etching systems, material deposition systems, and flat panel display etching systems. Due to the growing demands for cleanliness and high processing precision, there has been a growing need to reduce the amount of human interaction during and between processing steps. This need has been partially met with the implementation of vacuum transport modules which operate as an intermediate wafer handling apparatus (typically maintained at a reduced pressure, e.g., vacuum conditions). By way of example, a vacuum transport module may be physically located between one or more clean room storage facilities where wafers are stored, and multiple wafer processing modules where the wafers are actually processed, e.g., etched or have deposition performed thereon. In this manner, when a wafer is required for processing, a robot arm located within the transport module may be employed to retrieve a selected wafer from storage and place it into one of the multiple processing modules.
As is well known to those skilled in the art, the arrangement of transport modules to xe2x80x9ctransportxe2x80x9d wafers among multiple storage facilities and processing modules is frequently referred to as a xe2x80x9ccluster tool architecturexe2x80x9d system. FIG. 1 depicts a typical semiconductor process cluster architecture 100 illustrating the various chambers that interface with a vacuum transport module 106. Vacuum transport module 106 is shown coupled to three processing modules 108a-108c which may be individually optimized to perform various fabrication processes. By way of example, processing modules 108a-108c may be implemented to perform transformer coupled plasma (TCP) substrate etching, layer depositions, and/or sputtering.
Connected to vacuum transport module 106 is a load lock 104 that may be implemented to introduce wafers into vacuum transport module 106. Load lock 104 may be coupled to a clean room 102 where wafers are stored. In addition to being a retrieving and serving mechanism, load lock 104 also serves as a pressure-varying interface between vacuum transport module 106 and clean room 102. Therefore, vacuum transport module 106 may be kept at a constant pressure (e.g., vacuum), while clean room 102 is kept at atmospheric pressure.
Consistent with the growing demands for cleanliness and high processing precision, the amount of human interaction during and between processing steps has been reduced by the use of robots for wafer transfer. Such transfer may be from the clean room 102 to the load lock 104, or from the load lock 104 to the vacuum transport module 106, or from the vacuum transport module 106 to a processing module 108a, for example. While such robots substantially reduce the amount of human contact with each wafer, problems have been experienced in the use of robots for wafer transfer. For example, in a clean room a blade of a robot may be used to pick a wafer from a cassette and place it on fingers provided in the load lock 104. However, the center of the wafer may not be accurately positioned relative to the fingers. As a result, when the blade of the robot of the vacuum transport module 106 picks the wafer from the fingers of the load lock 104, the center of the wafer may not be properly located, or aligned, relative to the center of the blade. This improper wafer center-blade center alignment, also referred to as xe2x80x9cwafer-blade misalignmentxe2x80x9d or simply xe2x80x9cwafer misalignment,xe2x80x9d continues as the robot performs an xe2x80x9cextendxe2x80x9d operation, by which the blade (and the wafer carried by the blade) are moved through a slot in the processing module and by which the wafer is placed on pins in the processing module 108a, for example.
Even if there was proper original wafer-blade alignment when the wafer was initially placed in the exemplary processing module 108a, and even though the wafer may have thus been properly aligned during processing in the exemplary processing module 108a, the proper alignment may be interfered with. For example, electrostatic chucks generally used in the exemplary processing modules 108a may have a residual electrostatic field that is not completely discharged after completion of the processing. In this situation, the processed wafer may suddenly become detached from the chuck. As a result, the wafer may become improperly positioned with respect to the robot blade that picks the processed wafer off the chuck. Thus, when the blade of the robot of the vacuum transport module 106 picks the processed wafer off the chuck, the center of the wafer may not be properly located, or aligned, relative to the center of the blade. This wafer misalignment may continue as the robot performs a xe2x80x9cretractxe2x80x9d operation, by which the blade (and the wafer carried by the blade) are moved through the slot in the processing module 108a. Such wafer misalignment may also continue during a subsequent extend operation by which the wafer is placed in another one of the processing modules 108b, or in the load lock 104.
Wafer misalignment is a source of wafer processing errors, and is of course to be avoided. It is also clear that the amount of time the robots take to transfer a wafer among the modules (the xe2x80x9cwafer transfer timexe2x80x9d) is an amount of time that is not available for performing processing on the wafer, i.e., the wafer transport time is wasted time. Thus, there is an unfilled need to both monitor the amount of such wafer misalignment, and to perform such monitoring without greatly increasing the wafer transfer time.
However, a problem complicating such monitoring of wafer misalignment is that a wafer may be transferred from (or to) the one vacuum transport module 106 to (or from) as many as six, for example, processing modules, e.g., 108a. In the past, attempts to determine whether a wafer is properly aligned on the blade of a robot have included use of many sensors between adjacent modules. Sensors on opposite sides of a wafer transfer path have been located symmetrically with respect to the wafer transfer path. The symmetrically opposed sensors produce simultaneous output signals, and one data processor has to be provided for each such sensor. The combination of these factors (i.e., the possible use of six processing modules plus the vacuum transport module, the use of many symmetrically located opposing sensors per module, and the use of one data processor per sensor) result in increased complexity and the need for many costly processors for a cluster tool architecture. In view of the need to provide cluster tool architectures that are more cost-efficient, the incorporation of separate data processors for each sensor can make a system prohibitively expensive.
Another aspect of providing cluster tool architectures that are more cost-efficient relates to the cost of machining the modules and the load locks to provide apertures in which sensors, such as through-beam sensors, may be received. As the accuracy of such machining is increased to more accurately locate the sensors with respect to the robots, for example, there are increased costs of such precision machining. What is needed is a way of requiring less accuracy in machining the apertures for the sensors without sacrificing the accuracy of detections made using the sensors.
The use of such through-beam sensors also presents problems in the design of apparatus for monitoring wafer misalignment. For example, when a wafer moves through a light beam of such a through-beam sensor and breaks the beam, it takes a period of time (latency period) for the sensor to output a pulse indicative of the breaking of the beam. Since the wafer is moving relative to the sensor, and when the purpose of the sensor is to determine the location of the wafer, by the time the output pulse is generated (at the end of the latency period) the wafer will have moved from the location of the wafer when the beam was broken. The latency period is a source of errors in the use of the through-beam sensors. What is also needed then is a way of reducing the errors caused by the latency period of through-beam sensors.
In view of the foregoing, there is a need for methods and apparatus for wafer alignment that operate while the wafer is being transported without increasing the wafer transport time (e.g., without reducing the rate of transfer of the wafer among the modules or load locks). Such method and apparatus should not only reduce the number of data processors per sensor, but reduce the total number of data processors used for determination of wafer misalignment in an entire cluster tool architecture. Such method and apparatus desirably also require less accuracy in machining the apertures for the sensors, without sacrificing the accuracy of detections made using the sensors. Another aspect of the desired method and apparatus is to eliminate the latency period as a source of errors in using through-beam sensors to make wafer alignment determinations.
Broadly speaking, the present invention fills these needs by providing dynamic alignment of each wafer with a support blade that carries the wafer, wherein dynamic alignment apparatus and methods determine the location of a center of the wafer with respect to a center of the blade as the blade moves the wafer through a module port or slot from one module to another module. By determining the offset of the wafer relative to the blade, the robot can use this determined offset to enable precision alignment and placement in process chambers of the cluster tool architecture.
One aspect of the present invention is a method and apparatus for determining wafer misalignment that provides sensors operative while the wafer is being transported and without increasing the wafer transport time, that is, without reducing the rate of transfer of the wafer among the modules or load locks.
Another aspect of the present invention is the use of a calibration wafer of known physical characteristics to calibrate a blade, a robot, and newly machined apertures which receive wafer sensors. The calibration method and apparatus of the invention require less accuracy in machining the apertures for the sensors, without sacrificing the accuracy of wafer alignment determinations made using the sensors, because the calibration accurately determines the location of each sensor after the sensor has been inserted into the aperture. A calibration method uses the calibration wafer to calibrate a system for generating data indicating the position of a center of a wafer relative to a center of a blade of a wafer transport robot, wherein the wafer is provided with at least one edge.
The method starts by mounting the wafer transport robot adjacent to semiconductor manufacturing equipment having a port so that the robot moves the wafer through the port along a wafer transport axis. At least two sensors are spaced along the port on an axis that is transverse to the wafer transport axis. The sensors are tripped by the presence of the wafer edge and by the absence of the wafer following the presence of the wafer edge. Each time one of the sensors is tripped the tripped one of the sensors is effective to generate a separate data item. A calibration wafer of known dimensions is secured to the blade in a position centered with respect to the center of the blade. Data is captured as to the position of the sensors relative to the robot by causing the robot to move the calibration wafer through the port and past the sensors. The sensors generate the separate data items, each of the separate data items indicating the location of one of the edges of the calibration wafer as the calibration wafer moves past the sensors. An accurate determination is made as to the location of the sensor with respect to the robot by using the location of the robot corresponding to each separate data item, and using data as to the radius of the calibration wafer, and using the separate data items.
In another aspect of the present invention, only one data processor is needed regardless of how many sensors are provided per module and regardless of which of many modules is receiving or supplying a wafer. The method and apparatus of the present invention not only reduce the number of data processors per sensor, but reduce the total number of data processors used for determination of wafer misalignment in an entire cluster tool architecture. This advantage results in part from accounting for the latency period of through-beam sensors when positioning such sensors relative to the path of the wafer. In detail, the need for only one processor results from positioning such sensors along a transverse axis of a module slot in a non-symmetrical manner so as to assure that a first such sensor generates a transition signal and in response to the transition signal the robot position information related to that signal is stored before a second such sensor generates a next transition signal.
An apparatus having these characteristics is provided for generating data indicating the position of a center of the wafer relative to the center of a blade of a wafer transport robot as the blade moves the wafer at a controlled rate of transfer along a path that extends through a plane defined by a facet of a module of semiconductor manufacturing equipment. Initially, a sensor positioning axis extends in the plane and intersects the path. A first sensor is mounted in the plane, on the positioning axis, and spaced from the path by a first distance so as to sense the wafer moving in the path. The first sensor has a latency period between a first time of sensing the wafer and a later time at which robot position data is stored in response to a transition signal output by the first sensor to indicate the sensing of the wafer.
A second sensor is mounted in the plane, on the positioning axis, and spaced from the path by a second distance so as to sense the wafer moving in the path. The second distance is different from the first distance by an amount such that at the given rate the time between a first moment at which the wafer is sensed by the first sensor and a second moment at which the wafer is sensed by the second sensor is not less than the latency period.
An apparatus having these characteristics is also provided for generating data indicating the position of a wafer relative to a blade of a wafer transport robot as the blade continuously moves the wafer along a path that extends through a plane defined by one of a plurality of facets of a plurality of modules of semiconductor manufacturing equipment. A sensor positioning axis extends in each of the planes and intersects the respective path. A first sensor is mounted in each of the planes, on the respective positioning axis, and spaced from the respective path by a first distance so as to sense the wafer moving in the respective path. The first sensor has a first latency period between a first time at which the first sensor senses the wafer in the respective path and a later time at which robot position data is stored in response to a first transition signal output by the first sensor to indicate a first sensing of the wafer in the respective path.
A second sensor is mounted in each of the planes, on the respective positioning axis, and spaced from the respective path by a second distance so as to sense the wafer moving in the respective path. The second sensor outputs a second transition signal indicating a second sensing of the wafer in the respective path. For each second sensor with respect to each first sensor, the second distance is different from the first distance by a selected amount. That amount assures that a first moment at which the wafer moving in the respective path is sensed by the first sensor, plus the first latency period, is not later in time than a second moment at which the wafer moving in the same respective path is sensed by the second sensor. In this manner, before the second sensor senses the wafer in the respective path, the first transition signal is output by the first sensor in response to the first sensor sensing the wafer in the respective path and the robot position data is stored.
Accordingly, there is temporal spacing of the first and second transition signals output by the respective first and second sensors. An important result of the temporal spacing of the transition signals is that only one processor is needed for receiving each of the first and second transition signals. In other words, because the transition signals are not generated at the same time, there is no need for multiple processors that operate simultaneously to process the transition signals. Although the transition signals are temporally spaced, the wafer movement may continue without interruption, such that throughput of wafers through the system is not reduced.
Such apparatus is also provided for wafers having different physical characteristics, such as a 200 mm or a 300 mm wafer diameter. Of course modifications can be made to the apparatus to accommodate smaller or larger substrates. The apparatus generates data indicating the position of the center of the wafer relative to the center of a blade of a wafer transport robot as the blade continuously moves the wafer along a path that extends through a plane defined by one of a plurality of facets of a plurality of modules of semiconductor manufacturing equipment. A sensor positioning axis extends in each of the planes and intersects the respective path. The wafer may have either of a first and a second physical characteristic, such as the 200 mm diameter or the 300 mm diameter, for example. The robot may cause the blade and the wafer carried by the blade to move in an extend motion through the respective plane into the respective module, or to move in a retract motion through the respective plane from the respective module. A first sensor is mounted in each of the planes, on the respective positioning axis, and spaced from the respective path by a first distance so as to sense the wafer moving in the respective path. The first sensor has a first latency period between a first time at which the first sensor senses the wafer in the respective path and a later time at which robot position data is stored in response to a first transition signal indicating the sensing of the wafer in the respective path.
A second sensor is also provided for use with either the 200 mm diameter wafers or the 300 mm diameter wafers. For the 200 mm wafers, the second sensor is mounted in each of the planes, on the respective positioning axis, and spaced from the respective path by a second distance so as to sense the wafer moving in the respective path. The second sensor outputs a second transition signal indicating the sensing of the wafer in the respective path. For each second sensor with respect to each first sensor, the second distance is different from the first distance by a selected amount. That amount assures that a first moment at which the wafer having the first physical characteristic and moving in the respective path is sensed by the first sensor, plus the first latency period, is not later in time than a second moment at which the wafer having the first physical characteristic and moving in the same respective path is sensed by the second sensor.
In this manner, before the second sensor senses the wafer in the respective path, the first transition signal is output by the first sensor in response to the first sensor sensing the wafer having the first physical characteristic and in the respective path, and the robot position data is stored. As a result, for the wafer having the first physical characteristic there is temporal spacing of the first and second transition signals output by the respective first and second sensors.
For the 300 mm diameter wafers, the second sensor is also mounted in each of the planes and on the respective positioning axis, but is relocated so as to be spaced from the respective path-by a third distance. As relocated, the second sensor senses the wafer having the second physical characteristic and moving in the respective path. For ease of description, the relocated second sensor spaced by the third distance is referred to as the xe2x80x9cthirdxe2x80x9d sensor. The third sensor has a third latency period between a third time at which the third sensor senses the wafer in the respective path and a later time. The later time occurs once the third sensor outputs a third transition signal indicating the sensing of the wafer having the second physical characteristic and in the respective path and robot position data is stored. For each third sensor with respect to each first sensor, the third distance is different from the first distance by an amount such that a third moment at which the wafer having the second physical characteristic and moving in the respective path is sensed by the third sensor, plus the third latency period, is not later in time than a fourth moment at which the wafer having the second physical characteristic and moving in the same respective path is sensed by the first sensor.
Accordingly, before the first sensor senses the wafer having the second physical characteristic and in the respective path, the third transition signal is output by the third sensor in response to the third sensor sensing the wafer having the second physical characteristic and in the respective path. For the wafer having the second physical characteristic, the first and third transition signals are output by the respective first and third sensors in temporal spacing. In view of the provision of a plurality of facets and sensors on the plane of each facet, logic circuitry is used to combine all of the outputs represented by the transition signals from all of the facets through which the wafer may be moved.
A method aspect of the present invention also provides the benefit of requiring only one processor to process the transition signals. The method provides data indicating the position of the center of a wafer with respect to the center of a blade carrying the wafer, and includes an operation of mounting the wafer on the blade for movement with the blade along a path. There is also an operation o f providing a first sensor along a transverse axis that has a center at an intersection with the path, the first sensor being on one side of the center. A next operation provides a second sensor along the transverse axis and on the other side of the center, the second sensor and the first sensor being spaced by a selected distance.
The wafer is continuously moved along the path so that the first sensor is triggered by the wafer and generates a first transition signal and the second sensor is triggered by the wafer and generates a second transition signal. The need for only one processor results from placing each of the first and second sensors along the transverse axis according to a latency characteristic of the sensor so that the wafer moving through the port will be sensed by individual ones of the plurality of sensors at temporally-spaced times. The temporally-spaced times allow the first of the sensors to sense the wafer and generate a first transition signal, and allow the robot position data corresponding to each first transition signal to be stored, all before the second of the sensors senses the wafer and generates a second transition signal. Stated alternatively, the selected distance is selected to temporally space the moments in time at which the first and second sensors are triggered by the wafer so that the first transition signal is generated and the robot position data corresponding to each first transition signal is stored before the wafer triggers the second sensor.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.